High-Density Harmonic Drive Actuator With Integrated Slip Clutch
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Solution Overview
Problem
Existing actuators are bulky and heavy due to the need for additional hardware to support motor and transmission components, and they lack a compact and lightweight configuration suitable for orthotic devices, with commercial versions often being cumbersome and heavy due to over-torque protection mechanisms.
Innovation Solution
A high-density actuator design featuring a compact arrangement of a brushless motor, single-stage transmission, over-torque protection mechanism, and integrated torque sensor, with a concentric output stage bearing and custom slip clutch, utilizing conical roller bearings and a magnetic torque sensor for efficient torque measurement and minimal lateral torsion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If traditional actuators use additional hardware (bearings, levers, pivots) to support motor and transmission components, then the actuator can maintain structural stability and support loads, but the actuator becomes bulky and heavy
Solution Approach 1:
The patent combines the output stage bearing with the motor housing, integrating two previously separate components into one unified structure. The motor housing serves dual purposes: enclosing the motor and providing bearing support functionality, thereby eliminating the need for separate support hardware and reducing overall actuator weight and complexity
Solution Approach 2:
The motor housing is designed to perform multiple functions simultaneously: it encloses the motor components, provides structural support, and acts as a bearing carrier. This multi-functional design eliminates the need for dedicated support components, directly addressing the contradiction between weight reduction and structural stability
2Volume of moving object
If actuators are designed to be compact and lightweight, then the actuator size and weight are reduced, but the structural support and load-bearing capacity may be compromised
Solution Approach 1:
By merging the bearing function into the motor housing, the patent achieves compactness without sacrificing load-bearing capacity. The integrated design maintains structural integrity while reducing the volume required for separate support components, resolving the contradiction between compactness and strength
3Reliability
If commercial actuators include over-torque protection mechanisms (slip clutch), then the actuator is protected from damage under over-torque conditions, but the actuator becomes cumbersome and heavy
Solution Approach 1:
The torque limiting assembly is integrated into the existing actuator structure, sharing space with other components rather than adding separate protection hardware. This merging approach provides reliable over-torque protection while minimizing the weight increase that would normally accompany such safety mechanisms
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves a significantly lighter and more compact actuator with effective over-torque protection, reducing size and weight while maintaining high torque density and precise torque control, suitable for orthotic and prosthetic applications.
Implementation Method 1
a flexible sensor beam having a first extremity connected to the housing assembly and a sensor magnet positioned on the housing assembly, wherein displacement of a second extremity of the flexible sensor beam relative to the housing assembly measured by the sensor magnet is indicative of the torque applied by the high density actuator
Implementation Method 2
a sensor magnet positioned on the housing assembly, wherein displacement of a second extremity of the flexible sensor beam relative to the housing assembly measured by the sensor magnet
Implementation Method 3
a torque limiting assembly positioned around the torque transfer output configured to frictionally engage or disengage the brake pad and the band with the torque transfer output
Data Source
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AI summary
A high density actuator, comprising a housing assembly composed of a first housing element containing a motor stator and a second housing element containing a gear reduction mechanism, a rotational core positioned at the center of the housing assembly, the rotational core being composed of a motor rotor and a transmission input operatively connected to the motor rotor, a transmission output positioned between the transmission input and the housing assembly, the transmission output forming an actuator output, a torque transfer output operatively connected to the actuator output and a center shaft connected to the torque transfer output in its center and in rotational contact with the first housing element, the center shaft passing through the transmission output, rotational core and second housing element to ensure proper radial and axial alignment.